The present disclosure relates to an optical scanning device including a scanning lens which performs, on a surface to be scanned, imaging of a light beam that was deflected and scanned, and an image forming apparatus using the foregoing optical scanning device.
For example, a general optical scanning device that is used, for example, in laser printers and copiers includes a light source which emits a laser beam, a polygon mirror which reflects and deflects/scans the laser beam, and a scanning lens which performs imaging of the deflected/scanned laser beam on a peripheral surface (surface to be scanned) of a photoreceptor drum. As the scanning lens, a lens having a distortion (fθ characteristics) in which the angle of the incident light and the height of the image become a proportional relation is used. Moreover, the foregoing scanning lens is generally manufactured by molding a resin material in a metal mold.
While the scanning lens is sometimes configured from a plurality of lenses, it is also sometimes configured from one lens for the purpose of downsizing the device or reducing costs. As conventional technology, in an optical scanning device in which the scanning lens is configured from one lens, known is design technology of defining the relation of the entrance face and the exit face of the scanning lens in a main scanning direction cross section. Specifically, when a curvature radius near an optical axis of the entrance face facing the polygonal mirror is R1 and a curvature radius near an optical axis of the exit face is R2, the scanning lens is configured from a meniscus lens which is convex on the polygon mirror side and which satisfies a relationship of 0<R1<R2.
Nevertheless, upon using the scanning lens of the optical scanning device according to the foregoing conventional technology, there is a problem in that the optical performance is unstable, or the productivity is inferior. In other words, when the scanning lens satisfies the relationship of 0<R1<R2, the thickness of the scanning lens in the optical axis direction will become thinner from the center part to the end part in the main scanning direction. When a scanning lens having this kind of thin part is manufactured by molding, the shape tends to vary slightly in each molding process. Thus, the optical performance among the molded scanning lenses becomes unstable. This problem can be resolved by extending the cast molding time and the cooling time in the molding process. Nevertheless, a problem regarding the deterioration in productivity will naturally arise.
An object of the present disclosure is to stabilize the optical performance of the scanning lens.